Thermoplastic polymers, including thermoplastic elastomers, are used in many fields, for example in the electrical and electronics field, in the construction field, in building technology, in automotive production and in public transport vehicles. They have advantageous mechanical properties and good processability and chemical stability. One possible way of making such polymers flame resistant is the addition of halogen-containing flame retardants with antimony trioxide. A further possibility is the addition of halogen-free substances such as metal hydroxides, organic or inorganic phosphates or phosphonates, for example ammonium polyphosphates, together with synergistically active substances such as carbon sources and blowing agents.
The halogen-free flame retardants in particular are gaining increasing importance since in contrast to flame retardants which contain chlorinated or brominated organic compounds, they cause less fume evolution in case of fire and are as a rule classified as environmentally friendly. Among the fire retardant substances, derivatives of phosphoric acid, pyrophosphoric acid and the polyphosphoric acids are mainly used in halogen-free flame retardants. Ammonium and melamine derivatives of the aforesaid substances and piperazine phosphate and ethylenediamine phosphate have the property that when they are incorporated in moulding compositions they swell into voluminous protective layers at high temperatures and act as an insulating layer against a heat source. This property can be further reinforced by synergistically active substances. In contrast to the mode of action of halogen-containing flame retardants, the swelling, so-called intumescence, takes place without the evolution of substantial quantities of fumes.
The use of the aforesaid flame retardants in polyolefins often does not provide sufficient protection and in addition synergistically active substances such as for example carbon sources and blowing agents must be added. In order to ensure adequate effectiveness of such flame retardant compositions, a very high proportion of flame retardant must often be added to the polymer, which leads in particular to alteration of the mechanical and electrical properties of the polymer.
The previously particularly effective flame retardants include mixtures of ammonium polyphosphate with amines, such as for example mixtures with melamine compounds and/or pentaerythritol. Further well-known intumescent mixtures are based on ammonium polyphosphates in combination with THEIC (1,3,5-tris-hydroxyethylisocyanuric acid).
However the disadvantage of these mixtures consists in the fact that even after introduction into a polymer they display very high water solubility so that they are partially leached out and consequently their effect can no longer be obtained. Furthermore they have a low decomposition temperature, which already to some extent leads to decomposition of the flame retardant additive during the moulding of the plastic objects from the polymer to be protected. Furthermore in spite of improved effectiveness these mixtures must be used in high concentrations in a polymer as a result of which the processability and flexibility of the polymer is decreased.